Dry kiln apparatus



Nov. 29, 1955 A. R. PIERCE 2,725,224

DRY KILN APPARATUS Filed May 11, 1955 3 Sheets-Sheet 2 Wafer 5140,09

Arroz/Vex Nov. 29, 1955 A, R, Flr-RCE 2,725,224

DRY KILN APPARATUS Filed May 11, 1953 5 Sheets-fSheet 5 IN VEN TOR. A5er E @265 QZ/Www United States Patent- DRY KlLN APPARATUS Albert R. Pierce, West Covina, Calif.

Application May 11, 1953, Serial No. 354,116

2 Claims. (Cl. 263-40) This invention relates to dry kilns, and while it may be used in the equipment and operation of drying kilns used for any specific purpose, in the present specification it is described and illustrated as applied to kiln for drying and conditioning lumber.

In accordance with the present practice in dry kilns, the equipment usually includes heating coils for heating air that is then delivered into the kiln chambers. Steam boilers are also provided that deliver steam into the kiln chambers, and the hot air and steam are then mixed mechanically within the chambers of the kiln by powerdriven fans within the chambers.

The apparatus briefly described above is relatively exp by causing a direct loss in effective kiln operating time, and also a loss in heat consumption due to the cooling off of the hot kiln.

One of the objects of the present invention is to provide an efficient method for drying and conditioning lumber, that in addition to its eciency, can be carried on with relatively simple and inexpensive apparatus and the operation of which can be carried on continuously and with a minimum of heat losses due to shut downs of the kiln.

Another object'of the invention is to provide a method and means for effecting the direct supply of a hot, and moist, heating medium, to the kiln; and in the use of which the heating and introduction of the moisture into the drying medium can be very nicely regulated.

Further objects of the invention will become evident from a careful reading of the present specification, and a careful study ofthe accompanying drawings.

The invention consists in the novel parts and combinations of parts to be described hereinafter, all of which contribute to produce an eiiicient lumber drying and conditioning.

In the drawing:

Figure 1 is a horizontal section though the walls of a kiln showing the general arrangement of the equipment and the location of the furnaces, blowers, and the circulating system for the hot moist medium through the kiln.

Figure 2 is a vertical section taken about in the plane of the line 22 on Figure 1.

Figure 3 is a side elevation, and section through the furnace taken along the line 3 3 of Figure l, upon a larger scale than Figure l.

Figure 4 is a vertical cross-section taken on the line 4 4 of Figure 3.

Figure 5 is a diagrammatic view of the water system including the piping and spray nozzles and the controls therefor.

And, of course, any servicing to make repairs necessitates shutting down the kiln there- Mice the water spray nozzles and a portion of the radial pipe leading inwardly to the same.

Referring now to Figure 3, the fire box 1 of the furnace 2 that is illustrated, is of cylindrical form, and composed of suitable refractory material. As shown in the drawing, the right end of the iire box is open, and the left end has a transverse head 3 also of refractory material and provided with a Wide socket 4 of slot form located concentrically on the longitudinal axis of the iire box 1.

The socket carries a refractory burner S with a centrally disposed fuel duct 6, supplied with fuel oil or gas. For this purpose a good quality of butane may be used, or commercial gas from the city mains. The fuel is led into the rear of the duct through an adapter thimble 7 connected to an elbow on the axis of a tuyre 10 that supplies air to the air ports 11 of the burner.

The fuel is delivered to the inlet pipe 9 by a pipe connection 12 that leads down from a pressure-regulator assembly 13. This pipe connection 12 contains a hand valve 12a, an automatically controlled Water valve 14 is provided that is controlled by a solenoid 15, see Figure 5, and this solenoid in turn is controlled by a control instrument 16, the wires within which is controlled by the temperature in a Wet-bulb thermometer 19 and the other is controlled by the temperature in a dry-bulb thermometer 20.`

Referring now to Figure l,.it should be said that each chamber in the kiln carries a pair of these thermometers operating to give dual control of the valve 14. In Figure l, these two thermometers 19 and 2t) are indicated on the inner face of the wall 21 that separates the furnace room 22 from the chamber 23 of the kiln.

The wires for the circuits 17 and 18 pass through a duct 24 in the wall 21 and connect up to the control instrument 16 on the furnace room side of this wall 21. From this instrument 16 the Wires form a circuit 16a passing in a pipe conduit 25 over to the control-valve at 14 in Figure l.

Also, in Figure l, the corner of a second chamber 23a is shown at the right of the partition wall 21a that divides the chamber 23 from the 23a. The chamber 23a is provided on the side of the wall 21a with a wet-bulb thermometer 19a and a dry-bulb thermometer 2da which are counterparts of these instruments 19 and Z0 already referred to; and control circuit 17a and 18a for these instruments pass under or around the chamber 23 and through the Wall 21 at the duct 24a, emerging on the furnace room side of the Wall 21 Where they connect up to a controlling instrument 16a similar to the instrument 16, and the Wires from which pass through a piping conduit 25a similar to the conduit 25 already described. The circuit wires in the conduit 25a connect up to an instrument similar to the instrument 16 which is associated with another furnace 2a similar to the furnace 2, the latter of which is in a reversed position with respect to the furnace 2. The latter is completely illustrated in Figure 1. y

It should be understood that furnace 1a and all equipment co-operating therewith is substantially identical with that illustrated fully in connection with the chamber 23, so the specification now will be confined to the equipment associated with chamber 23.

Referring now to Figures l, 3, and 4, from the control valve 14, that delivers water to the spray nozzles 26 that I employ in each furnace. As illustrated in the drawing, I provide a delivery pipe 27a that receives a controlled water supply from the valveV 14, which is connected to an arcuate main-pipe 28, see Figure 4, that is bent on a slightly'l'arger radius thanthe inner surface of the iire box l.; and this arcuate pipe 28 is provided with T-connections 29, carrying radials 26a 'that carry the nozzles 26. The radials extend in a general radial plane towards the axis of the re box, but inclined inwardly and toward the end of :the tire box that carries the burner 5. With this arrangement, it will be evident that when the water linds exit through the spray nozzles 26 of the spray will be injected into the tire box in a direction against the direction of movement of the ame of burning fuel that is moving toward the outer end of the re box. In practice, the pipe 27 contains hand valves 30. These are shown in a horizontal extension of the pipe.

Referring no'w to Figure 5, the water supply is delivered through a water service pipe 31 at ordinary service, pressure, and in the present instance this supply pipe is connected to a T-connection 32 that supplies the water through a pipe 33 which is separated from the pipe 27 by the controlled valve 14 already mentioned. On the other side of the T 32 it is connected to a similar pipe 34 that delivers the water to the furnace 2a through a controlled Valve 14a that is similar to the valve 14 and actuated by its own solenoid 15a.

In the pipeline between the pipe 27 and the arcuate water ring 28 an electric heater 35 is provided, and

the water that passes up through this heater is delivered to it through a branch pipe 36, and from the heater the water passes to a'pipe 37 the lower end of which connects to an extension 27a of the pipe 27 already referred to, and this pipe vdelivers the heated water to the water ring 28; the heater elements 38 shown in dotted lines are supplied with current from a circuit 39 by means of a control device (not illustrated) which delivers the water from the heater 35 to the desired temperature; and in the present case, this temperature is slightly above the boiling point of the water. This temperature is preferably 250 degrees Fahrenheit. If theelectric current applied in the circuit 39 is an ordinary l1() volt circuit this circuit may be connected into a transformer 4t), the secondary coil of which steps up the voltage for the heating elements 38.

In order to enable flow of water to the spray nozzles 26 to be maintained for their protection when the sprays are not working by reason of the fact that the humidity in the kiln chamber has reached a desired point, I provide the pipe 36 with a hand operated valve 41, and in the pipe 27a a hand valve 42 is provided. These valves can be cracked to permit just sufficient how of water to the water rings 28 such as in the nozzles 26 to protect them from the furnace heat. Of course, the valve 42 would be closed most of the time, and always while the hot air and gases of combustion are being huinidied by the sprays.

In addition to this, I provide a by-pass pipe connection 43 around the controlled water valve i4, and this by-pass pipe is provided with a hand valve pipe 44 which is normally closed. However, this valve would be open at the same time that the valve 42 is open to pass a water dribble to the ring 28, and when for any reason the water heater is cut out of operation. The pipe 43 receives its water from the pipe 45 through a T-connection 46 that also supplies water to a by-pass pipe 43a for by-passing the other automatic water valve 14a.

Referring again to the furnace 2 and the pipe system for circulating the heating medium through the kiln; as

illustrated in Figure 3, the furnace has a jacket :47'which completely envelops the tire box. This jacket has a cylindrical body, the wall of which is separatedfrom'the ,4 outer face -or sur-face of -the fire box -1 -by an annular space 48 and includes an upper extension 49 communicating with the annular space 48. These parts operate as an inlet hood or receiver for effecting recirculation of the heating medium when it returns from the kiln chamber 23. The details of that will be described, hereinafter.

The jacket 47 is itself provided with lagging of insulation indicated by the dotted line 47a. `It also has a ilat head or transverse wall 50 which lies flatly against the outer faceofthevre box head 3 and Isurrounding the location of the head 3 there is an extension 51 of cylindrical wallof the saine ldiameter as'the 4'cylindrical part of the jacket 47. At the delivery4 end of the fire box a chamber 52 is formed the end wall S3 of which carries a substantially conical trunk connection 54, the small end of which is attached to an exhaust fan 5S. Its impeller withdraws the humidied gases of combustion from the chamber 52, and concentrates them as they'pass into 'a delivery main 56 which is composed of terra cotta pipe-sections. V'It carries the heating medium to a Y-c'on'nection'57 delivering the heating medium into two branch'conduits 58 and 59 of terra cotta that extend longitudinally of the chamber 23. These are located inline 'with-each other between two concrete tracks or ramps 60, on whichwheeledtrucks can be moved into the kiln chamber 23 from the end of the same that is broken way, at which'point a doorway (not illustrated) is providedfor the'trucks to pass The main S6 is composed of a continuous closed pipe with its sections connected together, end to end.

For the purpose of distributing the heating medium along the longitudinal axis of thechamber the branch pipes 53 and 59 are composedof short lengths v61 of'pipe which are in axial line with each-'other but spaced apart to form gaps 62 through which the medium can escape into the interior of thechamber l23. In order to facili` tate this escape, I prefer to iplacethe Asections 61 in a tilted up position toward the deliveryend of the branch lines 58 and 59. This is illustrated in 'Figure 7. The advantage of this is that the delivery end of this'pipe section 61 is slightly elevated above the inlet end of the pipe section that is receiving most of the current of heating medium that is flowing through.

The furnace 2a for the chamber 23a also has'an exhaust fan 55a which cio-operates with it in the vsame manner as the exhaust fan 55 co-operates with its furnace. The exhaust fan 55a delivers the heating medium through a continuous closed delivery main 63 of terra cotta pipe which passes completely through or under the chamber 23 and past the partition wall v21a intothe farchamber 23a; and in that chamber the main 63 connects to branch pipes (not illustrated) but which are similar to -the branch pipes 58 and 59 and are associated with eachother in the same way as illustrated in'cha'mber 23.

The exhaust system of piping for returning the heating medium to both the furnace 2 and 2a are substantially alike, and the system for chamber 23 will -now be described. This system includes a return main 64 which is composed of continuous closed pipe, 'that is fed with returning hot medium through two return branches 65 and 66 that connect to a Y 67 'at the inlet end of the main 64. These branches 65 are composed of short pipe sections 68 that are supported near together but set with their adjacent ends spaced apart to form gaps 69 through which the circumambient hot medium may enter from the interior of the chamber 23.

The pipes or inlet branches 65 and 66 are located near the partition Walls 21a. However7 another pair of return branches 70 and 71 are employed located adjacent to the wall 21 and which deliver their return current as a lateral connection into the return main'64 near the chamber 49 and substantially in line with it.

This return branch 70 is composed of short sections of spaced pipe'arranged Vtoform inlet "gaps as indicated in Figure 8.

The return movement of the spent heating medium is augmented by the action of the current of air that flows into the fire box 1 through the tuyere 5, through which a continuous current of air is entrained by the action of a blower 72 which delivers the blast for the burner into the tuyere 10. This blast accelerates the ow of the gases of combustion and air forwardly and through the chamber 52, and co-operates with the exhaust fan 55 to maintain a partial vacuum in the chamber 52; and by reason of this the return medium that arrives in the chamber 49 is entrained and drawn into the conical duct 54.

Both the chambers 23 and 23a have air vents such as the vent 73 shown in Figure 2. The opening through which is closed and regulated by a buttery valve 74. This valve, of course, is equipped with control means (not illustrated) for operating it from a position in the re room.

For driving the shafts 7S of the blowers 55 and 55a two electric motors are provided with driving belts 77 running over belt pulleys 78 on their shafts.

As indicated in Figures 1 and 2, the kiln chambers are provided with horizontal rails 79 disposed transversely to the ramps 60 and their upper faces are flush with the upper faces of the ramps. These ends of these rails are supported in the cement foundation walls 80, and in the cement ramps 60. These rails may be I-beams or channels, and operate to support stacks of lumber built up on them in the usual Way with ample spaces through the stacks for permitting free circulation for the heating medium through the stacks. However, this is not illustrated, as it is common practice in drying kilns.

In accordance with my invention, in practicing the method, after stacking the lumber in the kiln chambers, I start up the furnace and the water heater 38 which supplies water to the spray nozzles 26; and at the same time all the blowers are started up so that the gases of combustion and admitted air supplied to the furnace lirebox by the blower 10 are moved into the kiln chamber.

The control for the electric water heater (not illustrated) is set by hand to cause delivery of water at approximately 250 degrees Fahrenheit to the nozzles. As this water is under approximately 60 lbs. p. s. i. commercial line pressure, as soon as the spray passes from the nozzles 26 into the fire-box, which is not under pressure, it immediately vaporizes on account of its latent heat at 60 lbs. pressure. The water is vaporized into dry steam immediately at 250 degrees Fahrenheit. This action, of course, is accelerated by the ame, and the high temperature in the fire-box, the result is that in an extremely short period of time the heating medium will be raised to a very high degree of saturation with the moisture. The circulation through the lumber, of course, quickly heats the lumber but without drying its exterior. In this way the sap in the lumber becomes heated and becomes more or less dissolved in the moisture that is passing into the lumber in the heating medium. As this operation progresses, the wet and dry bulb thermometers 19 and 20 co-operating with their recording control instruments 16 and 16a control the water valve 14. They are set by hand to the limit of saturation desired, and shut oif at that point. But may be adjusted to supply additional water when necessary to increase the humidity and less water when the humidity arrives at the desired point with the kiln compartment. This heating is continued for a sufcient period of time in accordance with ordinary proved dry kiln practice, after which the furnace and blowers are shut down.

The regular procedure used on kiln drying lumber is followed through the drying cycle. That is, as the lumber becomes dryer, more heat and less humidity is forced into the kiln; that is done by normally setting the heat and humidity controller from time to time to the driest heat and humidity that you desire in the kiln based on the dryness of the lumber at that time. The dryness of the lumber is determined by the approved methods used by all kilns, so is not necessary to explain.

When the dryness tests show that the lumber has arrived at the desired moisture content, I start a period of conditioning it. By this I mean that I lower the heat in the kiln and raise the humidity from the percentage that I had in the kiln automatically at the end of the firing, which is generally 30 percent up to 85 or 90 percent. The time period of this conditioning depends entirely upon the species of wood. It will range from 24 to 72 hours. My reason for doing this is that all species of lumber during the drying cycle will develop a small amount of stress due to surface hardening. By this conditioning this stress is all relieved and all of the lumber becomes equalized in moisture content.

The above conditioning operation is accomplished very readily with the equipment that I have developed. All that is necessary to do is to turn the burner flame to a very low point and open up the water spray controls so that a maximum of spray is entering the heating chamber which vaporizes and is forced into the kiln compartment. When I consider that the conditioning treatment has been suicient I shut oi all heat, power and humidifier units, open the kiln door and remove the lumber.

Many other embodiments of the invention may be resorted to without departing from the spirit of the inventon.

I claim as my invention, and desire to secure by Letters Patent:

1. In apparatus for drying lumber in a kiln, the combination of a fire box, means for maintaining a iiame and an air jet projected into the fire box, means for maintaining a confined supply of water, and for raising the temperature of the same to a controlled temperature of approximately 250 degrees Fahrenheit, means for spraying the same at that temperature into the lire box, means for circulating the air and gases of combustion thereafter through the kiln, said circulating means including short sections of ducts laid with their ends adjacent to each other and spaced apart so as to form outlets permitting passage of the hot gases and air into the kiln at points dispersed throughout the area of the kiln, and automatic means for regulating the quantity of water admitted to the spray in accordance with the degree of humidity existing in the kiln.

2. Apparatus for drying lumber in a kiln, according to claim 1, in which the ends of said pipe lengths located down stream with respect to the direction of flow of the current through them are inclined upwardly above the mouths of the pipe lengths taking the current, so that a circumferential gap area between the pipe lenghts delivering the flow is formed through which the hot gases escape into the kiln chamber while flowing in the same general direction as said current.

References Cited inthe le of this patent UNITED STATES PATENTS 664,751 Hollingsworth Dec. 25, 1900 1,050,151 Loomis Jan. 14, 1913 1,339,705 Hirnrod May 11, 1920 1,469,976 Walsh Oct. 9, 1923 1,749,451 Strong Mar. 4, 1930 2,143,505 Arnold Jan. 10, 1939 2,285,718 Isaacson June 9, 1942 2,524,272 Sage Oct. 3, 1950 2,524,331 Rysdon Oct. 3, 1950 2,538,888 Smith Ian. 23, 1951 FOREIGN PATENTS 488,495 Germany Dec. 28, 1929 OTHER REFERENCES Kiln Drying Softwoods by Harry D. Tiemann. Forest Products Laboratory Report R702. Published April 1925, revised August 15, 1931. 14 pages, pages 4 to 7 relied on. 

